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used in amine systems with a circulation rate greater than 500 gpm. String-wound cotton car-
tridge filters also tend to deform when subjected to pressure and heat differentials and unload
fines back into the amine solution. String-wound cotton cartridge filters made from recycled
material should be avoided because they may contain oils and surfactants which can cause
foaming (Pauley, 199 1 ; Bacon, 1987). According to Table 3-7, conservative design would
indicate that string-wound cotton cartridge filters with a nominal 5 to 10 micron rating be
sized on the basis of 1 to 2 gpm/ft2 of external surface. String-wound cotton cartridges used
for amine service should be made from virgin cotton, be surfactant free, and contain no
residual cottonseed particles.

Proprietary Cartridge Filters

Major filter vendors supply proprietary filter cartridges that are specifically designed for
amine service. These filters are dimensionally stable under increasing differential pressure
because they are made from extrudable polymers such as polypropylene. Proprietary car-
tridge filters often have an “absolute” rating because the thickness of the polymer can be
carefully controlled, and they usually have higher capacities (in terms of gpm/ft2 of external
surface) than string-wound cartridge filters. Proprietary filter cartridges are usually made of
specially engineered materials and often incorporate unique design features to increase dirt
holding capacity and throughput. For example, the radial pleated cartridge filter depicted in
Figure 3-23 has a distinctive pleated design which provides 33 ft2 of filter surface for every
ft’ of cartridge external surface. Due to these special design features, it is virtually impossi-
ble to compare one proprietary filter cartridge to another without plant test or operating data.
Pauley (1991) and Pauley et al. (1988, 1989A, B) review the merits of proprietary car-
tridge filters. Suggestions for specifying, selecting, operating, and maintaining cartridge fil-
ters intended for amine service are found in papers by Ballard and von Phul (1991) and Bat-
lard (I 986A2, B). Factors that should be considered in selecting an amine filter include

Figure 3-23. Proprietary meltblown polypropylene microfiber filter cartridge for amine
service. Radial pleated design provides 33 ft2 of filter surface per ft2 of external
cartridge surface. Courtesy 3M Filter Products